Nest co-creator Tony Fadell isn't focused solely on making intelligent thermostats and smoke detectors. He recently unveiled Actev Motors, a company whose inaugural Arrow Smart-Kart promises to give kids a taste of what smart cars are like. The electric go-kart includes GPS, a and WiFi to keep junior drivers safe. Parents using a mobile app can geofence the kart's driving area, limit the top speed or hit a stop button in an emergency. In other words, even younger kids (5- to 9-year-olds are the main targets) can motor around without getting in over their heads. There's also a proximity sensor to automatically prevent accidents.